Nano- or micro-encapsulation is used in a variety of different applications where there is a need to deliver, apply, or release an active material including a fragrance, flavor, and malodor counteraction agent to a target area in a time-delayed or controlled manner. Various techniques for preparing capsules are known in the art and are used, depending on the contents to be encapsulated, the environment in which the capsules should retain their integrity and the desired release mechanism.
Interfacial polycondensation is a known technique for preparing capsules and versatile capsule wall materials are used including polyureas and polyurethanes (WO 2011/154893, WO 2012/107323, US 2011/0077188, U.S. Pat. Nos. 5,635,211, 6,586,107, and 6,797,670). Such wall materials are produced by having a first phase which is water-immiscible and includes a polyfunctional isocyanate, i.e., a polyisocyanate having two or more isocyanate groups, and a second aqueous phase which includes (i) a polyfunctional alcohol (i.e., a polyol) having two or more —OH groups for obtaining a polyurethane capsule wall, or (ii) a polyfunctional amine (i.e., a polyamine) having two or more —NH2 and/or —NH groups for obtaining a polyurea capsule wall.
If the active material to be encapsulated is hydrophobic, it will be included in the water-immiscible phase, thereafter the two phases are mixed by high shear mixing to form an oil-in-water emulsion. In this emulsion, the polycondensation reaction will take place. Thus, the small droplets of the water-immiscible phase will be surrounded by the capsule wall formed by polycondensation of the isocyanate and the polyalcohol or polyamine as starting materials. Conversely, if the material to be encapsulated is hydrophilic, it will be included in the aqueous phase and the mixture of the two phases converted into a water-in-oil emulsion. The polycondensation reaction will then form capsule walls surrounding the droplets of water-miscible phase. Suitable emulsifiers are often utilized to aid in the preparation and stabilization of the emulsion.
Suitable raw materials and processes for preparing capsules by polycondensation are described in U.S. Pat. No. 4,640,709 and the literature described therein. As is exemplified therein, and also in U.S. Pat. No. 6,133,197, polyurea and polyurethane capsules are often used for rugged applications, such as for encapsulation of agrochemicals, e.g., herbicides and pesticides, where slow time-release is desired to set the agents free. For such applications, the capsules also require a relatively high mechanical strength. For the polycondensation reaction, suitable diisocyanate and symmetrical triisocyanate starting materials are disclosed in the prior art.
WO 2011/154893 discloses a process for the preparation of capsules, which includes mixing at least one aliphatic polyisocyanate and of at least one aromatic polyisocyanate, wherein the molar ratio between the two polyisocyanates is between 75:25 and 20:80.
WO 2013/000587 discloses a process for the preparation of polyurea capsules, which includes dissolving at least one polyisocyanate having at least two isocyanate functional groups, in a perfume to form a solution; adding to the solution an aqueous solution of an emulsifier or of a colloidal stabilizer; and adding to the mixture to 3,5-diamino-1,2,4-triazole to form a polyurea wall.
U.S. Pat. No. 5,304,448 describes an encapsulated toner composition using reaction of amino acids and polyisocyanates.
Known polyurea or polyurethane capsules face various issues, e.g., low olfactory intensity, low stability, and high toxicity. Their deposition to target surfaces is also problematic.
There is a need to develop a safe, stable, and high efficient capsules for use in laundry, washing, cleaning, surface care and personal and skin care. For such applications quicker and easier release and/or less mechanical strength are often desirable. Also, it would be desirable to more precisely influence the capsule wall permeability and other capsule wall properties to achieve the desired release profile and consumer benefits.